The present invention relates to a new and distinct cultivar of Heuchera and given the cultivar name of ‘TNHEUGB’. Heuchera is in the family Saxifragaceae. Heuchera ‘TNHEUGB’ originated as a controlled cross using Heuchera ‘B107-3’, a proprietary, unpatented, unnamed seedling as the seed parent, and Heuchera ‘Macks Silver’, a proprietary, unpatented, unreleased seedling as the pollen parent. These parents are a result of breeding using Heuchera villosa with proprietary hybrid lines. Heuchera ‘TNHEUGB’ was bred to be a landscape plant with a large habit and large leaves for sun or shade. The trademark designations is ‘Grande™ Black.’
Compared to the seed parent, Heuchera ‘B107-3’, the new cultivar has larger, black leaves rather than silver leaves and a larger habit.
Compared to the pollen parent, Heuchera ‘Macks Silver’, the new cultivar has black leaves rather than silver leaves, a larger habit, and more crowns.
Compared to Heuchera ‘TNHEUNEB’, U.S. Plant Pat. No. 30,583, the new cultivar has a taller habit and black to purple leaves that are larger, more lobed, and wavier.
Compared to Heuchera ‘Mocha’, U.S. Plant Pat. No. PP18,386, the new cultivar has more glabrous leaves that are purple black to black rather than brown.
This new Heuchera is uniquely distinguished by:                1. purple black to black leaf color,        2. large leaves with slightly ruffled and rounded lobes,        3. very light pink flowers on upright flowering stems,        4. performing well in sun or shade,        5. a large, tall mounding habit with an excellent crown count, and        6. excellent vigor.        
This new cultivar has been reproduced only by asexual propagation (tip cuttings and tissue culture using growing tips). Each of the progeny exhibits identical characteristics to the original plant. Asexual propagation in 2015 by cuttings and tissue culture using standard micropropagation techniques with terminal and lateral shoots, as done in Canby, Oreg., shows that the foregoing characteristics and distinctions come true to form and are established and transmitted through succeeding propagations. The present invention has not been evaluated under all possible environmental conditions. The phenotype may change with variations in environment without a change in the genotype of the plant.